Inkjet technology typically utilizes radiation-curable inks, namely, ultra-violet (UV) sensitive inks. Printing apparatuses thus include, inter alia, a printing head assembly and a curing assembly (radiation source). The motion of the curing radiation source is synchronized with the motion of the printing head so as to sequentially apply curing to the previously sequentially printed locations.
The curing radiation source may be accommodated at a certain distance from a printing head and move together with the printing head with respect to a recording medium (substrate) along a printing line (across the substrate). Alternatively, a curing radiation source may be stationary mounted and equipped with optics (mirrors) movable together with a printing head.
U.S. Pat. No. 6,145,979 discloses an ink jet printer for forming an image on a moving substrate. Here, an ink curing apparatus has a radiation source stationary mounted outside the printer, and the curing radiation source is optically coupled to a mirror or a radiation-emitting head that directs the radiation to a desired location downstream of the printing head.
U.S. Pat. No. 6,454,405 discloses an ink-jet applicator using UV-curable ink. The applicator includes a print head, a guide operably secured to the print head housing to guide it across a medium being imprinted, a UV light source at one end of the guide and a mirror carried by the print head housing and oriented to reflect the UV beam onto the UV curable coating deposited by the print head. This technique is aimed at reducing the mass required to be added to the print head by the UV curing station.
Another technique aimed at reducing the mass of the printhead, in an inkjet printer utilizing radiation curing system, is disclosed in U.S. Pat. No. 6,447,112. According to this technique, the radiation source moves independently of the printhead to provide the desired electromagnetic curing energy to the printed ink.
In some material deposition processes, multi-stage UV curing is used:
U.S. Pat. No. 3,943,046 describes a UV curing process and apparatus for polymerizing oxygen-inhibited UV photopolymerizable resin-forming material, such as a film. This is implemented by using a pair of UV light sources, one being a flash photolysis source, and the other being a sustained photolysis source.
U.S. Pat. No. 4,048,036 describes a method of producing oxygen inhibitable UV curable coatings. Here, a desired flatting is obtained when films of oxygen inhibitable UV curable coating compositions containing flatting pigment are exposed to UV light, first in an oxygen containing atmosphere and then in a substantially oxygen free atmosphere.
U.S. Pat. No. 4,165,265 discloses a multi-stage irradiation method of curing a photocurable coating composition. Here, actinic radiation is used in the presence of air. The initial step involves irradiation with actinic radiation having wavelengths 185-500 millimicrons with dominant wavelength or wavelengths between 380-420 millimicrons, and the subsequent step involves irradiation with another actinic radiation of wavelengths within the same range as those of the radiation used for the initial step, but having dominant wavelength or wavelengths within a range shorter than those of the radiation used therefore. The initial irradiation is effected so as to cure the lower part of the coating layer with the surface portion thereof left uncured, and the subsequent irradiation leads to the full cure of the surface portion thereof.
U.S. Pat. No. 4,313,969 discloses a method and apparatus for providing low gloss and controlled gloss radiation cured coatings. According to this technique, a radiation curable coating of a composition including inert particulates is first irradiated with curing radiation of wavelength to which the coating is responsive but having no distribution beneath 300 nm, and is subsequently irradiated with curing radiation of wavelength to which the coating is responsive including radiation at wavelength beneath 300 nm. Gloss control is achieved by adjusting the spectral distribution, the intensity or the dose of the initial radiation, or by adjusting the time interval between the initial and the subsequent radiation steps.
U.S. Pat. No. 4,411,931 discloses a three-stage UV curing process for providing accurately controlled surface texture, particularly are useful as floor and wall coverings. A UV-curable substrate is initially exposed to long wave length light of low intensity, thereby causing the bottom portion of the substrate to gel while leaving the top surface essentially unaffected. The first stage irradiation is followed by irradiation with shorter-wave length UV light under an inert atmosphere, thereby causing the surface of the substrate to gel. The final stage of the curing process involves conventional exposure to strong UV light whereby the entire structure is cured to give a product having finely controlled surface texture.
U.S. Pat. No. 5,585,415 discloses pigmented compositions and methods for producing radiation curable coatings of very low gloss. This technique utilizes inclusion of a combination of photoinitiators having an acylphosphine oxide photoinitiator and a second photoinitiator such as an acetophenone derivative. The coating is first exposed to ionizing radiation (e.g., electron beam) in air, and then exposed to actinic radiation (ultraviolet light) in an essentially inert atmosphere.
EP 1072659 discloses a composition and process for providing a gloss controlled, abrasion resistant coating on surface covering products. The composition is cured to create a wearlayer surface, preferably on a floor covering product. The surface covering product is prepared and then the coating is partially cured by exposure to low peak irradiance UV light in either ambient or inert air, followed by fully curing the coating with high peak irradiance UV light in inert atmosphere to form a low gloss abrasion resistant wearlayer surface. Alternatively, the single-step exposure of the composition to high peak irradiance UV light in ambient atmosphere is used.